Long-time residents have been baffled by the phenomena, which has, in as little as four weeks, instilled an almost eerie feel to the familiar backdrop.

Among them, is Lake Cathie photographer and blogger Brett Dolsen.

Mr Dolsen has been documenting the distinct browning and dieback of the once flourishing canopy for the past few weeks.

The foreign foliage colour on North Brother, Middle Brother and South Brother mountains, he believes, is cause for concern.

"While some of this change can be expected from the prolific flowering of Eucalyptus trees this year, closer inspection reveals that many trees are dying or suffering extreme browning and loss of foliage," Mr Dolsen said.

In many parts of the mountains, a once vibrant sea of green has been replaced by suffering plants, stony surfaces and dying scrub.

He said the current situation, again puts into question the impact climate change could be having on local ecosystems.

"It concerns me, because it's basically starting to look like a bare mountain top," said Mr Dolsen, who has never seen anything like the prolific drying on Middle Brother mountain in more than three decades of living in the Hastings. "It would be fair to say the mountain has dried up."

Area manager for the Manning Hastings National Parks and Wildlife Service Steve Atkins said at this stage, there was no definite explanation for the situation.

He did point to studies, however, exploring the relationship between dry weather and heat-induced forest dieback and mortality.